Hello, help me please

Hello. Tell me the answers to my questions, please:

  1. Hotkey to move an object to the trash.
  2. How to make a note/a bookmark.
  3. When I save a project, a strange additional file appears inside the project. I must have imported it inside the project somehow and now I don’t know how to get rid of this file. Help me get rid of this phantom))). I’m attaching the drawing.
    Thanks! My English may not be very good.